I have googled and googled and cannot seem to find an answer for this (at least not a "I am doing this and it works/doesnt work"-answer).
If I buy a new Mac Mini and install boot camp (W7) and XBMC,will I then be able to bitstream TrueHD and DTS-Master to my processor? I would very much like to hear from someone who have actually done this.
Check out the Mac Sub forum: http://www.avsforum.com/f/115/htpc-mac-chat
There's a couple/few threads regarding Mac Mini / Bootcamp / Win7 / XBMC / HD audio. It's about as clear as mud but the general consensus is that it is possible. It may depend on what model you have; I've read the 2012 model with Intel i5 Ivy Bridge HD4000 is confirmed to work.
FWIW, I'm in the same boat. I have a 2012 Mini. I'm still putting my library together and haven't tested HD audio yet. I should be able to move the Mini from my work desk to my theatre in another week or so and then I'll check.